Method of making an encapsulated transducer with an alignment plug

ABSTRACT

The encapsulated transducer ( 10 ) includes an injection molded encapsulation ( 20 ) having a front end ( 22 ) and a back end ( 24 ). The encapsulation ( 20 ) ensconces a sensing element ( 40 ) proximate the front end ( 22 ) and a portion of a cable ( 60 ) which extends from the back end ( 24 ). The sensing element or coil ( 40 ) is electrically and mechanically connected to the cable ( 60 ) by a pair of suitably sized front and rear ferrules ( 80 ), ( 90 ) secured to a center and coaxial conductor ( 66 ), ( 70 ) of the associated cable ( 60 ) thereby forming a coil and cable assembly ( 110 ). At least the rear ferrule ( 90 ) includes a shoulder ( 100 ) for firmly anchoring the coil and cable assembly ( 110 ) within the encapsulation ( 20 ). In addition an injection molding process provides the durable encapsulation ( 20 ) which bonds with a dielectric ( 68 ) of the cable ( 60 ) and symmetrically locks the coil and cable assembly ( 110 ) therein.

This is a continuation of application Ser. No. 08/542,532, filed Oct. 13, 1995, and issued on Jan. 27, 1998, as U.S. Pat. No. 5,712,562.

FIELD OF THE INVENTION

The present invention relates generally to an encapsulated transducer with an alignment plug and, in particular, to an encapsulated transducer substantially impervious to any mechanical, physical or chemical aggressions from the surrounding environment and a method of manufacturing such transducer which is used to monitor vibration of rotating and recipocating machinery, temperature sensing and the monitoring and sensing of other physical phenomenon.

BACKGROUND OF THE INVENTION

Monitoring and diagnosing the status of rotating and reciprocating machinery start with accurate and dependable measurements from a transducer and its associated electronics and then precede to other sophisticated analyzing apparatus for reduction and display. One such transducer is a proximity transducer which may be utilized for, inter alia, monitoring the vibration characteristics of a rotating shaft of a machine. In this environment, the transducer must operate under very adverse physical, chemical and mechanical conditions and it is often very difficult to replace such transducers. Thus, there is an ongoing effort to make the proximity transducer one of the most reliable parts of the monitoring system.

Typically, the proximity transducer, in conjunction with associated electronics, outputs a signal correlative to the spacing between an object or “target” (the rotating shaft of the machine) and a sensing coil of the proximity transducer. It is critical that the length or spacing between the target and the sensing coil of the proximity transducer remains within the linear range of the transducer for providing accurate and reliable measurements when in operation. Thus, one hallmark for providing accurate and reliable measurements relies on providing a transducer which is impervious to the predations of the environment and which does not consume an inordinate amount of the linear range of the transducer.

The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.

U.S. PATENT DOCUMENTS DOCUMENT NO. DATE NAME 2,361,348 October 24, 1944 Dickson et al. 2,890,505 June 16, 1959 Brand 3,932,828 January 13, 1976 Plunkett et al. 4,000,877 January 4, 1977 Shead et al. 4,162,138 July 24, 1979 Byrne 4,377,548 March 22, 1983 Pierpont 4,408,159 October 4, 1983 Prox 4,419,646 December 6, 1983 Hermle 4,470,786 September 11, 1984 Sano et al. 4,680,543 July 14, 1987 Kohen 4,829,245 May 9, 1989 Echasseriau et al. 4,954,307 September 4, 1990 Yokoyama 4,959,000 September 25, 1990 Giza 5,016,343 May 21, 1991 Schutts 5,018,049 May 21, 1991 Mehnert 5,021,737 June 4, 1991 Schutts 5,039,942 August 13, 1991 Buchschmid, et al. 5,049,055 September 17, 1991 Yokoyama 5,122,046 June 16, 1992 Lavallee et al. 5,133,921 July 28, 1992 Yokoyama 5,138,292 August 11, 1992 Forster 5,147,657 September 15, 1992 Giza 5,151,277 September 29, 1992 Bernardon, et al. 5,182,032 January 26, 1993 Dickie et al. 5,226,221 July 13, 1993 Kilgore 5,240,397 August 31, 1993 Fay et al. 5,252,051 October 12, 1993 Miyamoto et al. 5,351,388 October 4, 1994 Van Den Berg, et al. 5,376,325 December 27, 1994 Ormson FOREIGN PATENT DOCUMENTS DOCUMENT NO. DATE COUNTRY UK 1 313 748 April 18, 1973 Great Britain UK 1 353 603 May 22, 1974 Great Britain JA-139710 August 6, 1978 Japan WO 84/03794 September 27, 1984 PCT FR 2576-245-A July 25, 1986 France JA 6-37130-A October 2, 1994 Japan

The two patents to Schutts and the patent to Van Den Berg, et al. reflect assignee's ongoing commitment to providing an accurate sensor which is impervious to predations of the environment.

The French patent to Jaeger teaches the use of a method and apparatus for injection molding of an elongated detector with a sensor at one end. One end of the detector is supported by the mold while the sensor end is engaged by a centering sleeve (130). The centering sleeve (130) terminates in a piston (132) which is mobile in a cylinder (126) and slides about a fixed rod (138). Thermoplastic is injected into the mold and the centering sleeve is removed from the sensor when the injection process is only partially complete.

The Japanese patent to Kawakami teaches the use of sealing a semiconductor chip by transfer molding. A semiconductor chip (4) is mounted on a carrier (1) and is held at a fixed position via mobile pins (17) and (18). The mobile pins (17) and (18) are movably fitted to a top force (11) and a bottom force (12) for freely advancing or retracting the pins into and out of the cavities (15) and (16). While the pins (17) and (18) are in contact with the carrier (1), a resin (20) is injected into the cavities (15) and (16) through gates (13) and (14) and the pins (17) and (18) are gradually retracted in accordance with the injecting state of resin (20).

The patent to Yokoyama teaches the use of an apparatus for manufacturing plastic encapsulated electronic semiconductor devices. A support pad (11) is firmly fixed by first and second sliders (24A) and (24B) and also by mold halves (19) and (20). The first and second sliders (24A) and (24B) are moved outwardly of a cavity (25) when the cavity is half filled with the plastic encapsulating material. Spaces, which are formed after movement of the sliders, are filled with the plastic encapsulating material directly poured through a gate (23). It should be noted that the sliders (24A), (24B) perform two functions in the cavity (25). The first function is to firmly grasp a thin end portion of the support pad (11) thereby fixing same in position and the second function is to narrow a passage through the gate (23).

The patent to Pierpont teaches the use of a method for encapsulating an electrical component having radial leads. A large multi-cavity mold is loaded with a plurality of horizontal radially leaded capacitors. The closed mold grips the leads (15). A top pin (25) pushes each component body downward a predetermined degree so that each body is left in about the same position within the corresponding mold cavity. A bottom pin (28) then pushes each component body upwardly only slightly above a center of the mold cavity so that upon bottom pin withdrawal, stresses within the lead wires of the electrical component cause the component bodies to spring back just to the mold cavity center portion. Molding resin is then introduced.

The other prior art listed above, but not specifically discussed, teach other sensor devices and molding processes and further catalog the prior art of which the applicant is aware. These references diverge even more starkly from the references specifically distinguished above.

SUMMARY OF THE INVENTION

The present invention is distinguished over the known prior art in a multiplicity of ways. For one thing, the present invention provides a transducer including a protective seamless encapsulation ensconcing a sensing element at one end and a cable extending out of the other end. In addition, the sensing element is symmetrically disposed about a long axis of the transducer and the seamless encapsulation includes an integrally formed protective wall having an uniform thickness along a forwardmost portion of the sensing element. The sensing element is electrically coupled to the cable for transmitting signals from the sensing element to an electrical processing unit. The signals can be correlative of, for example, machine vibration.

Preferably, the sensing element is in the form of a sensing coil having a front face, a back face, and a body having an outer surface and a center void extending through the body. The body extending between the front face and the back face. The sensing coil further includes at least a first lead and a second lead extending from the sensing coil and separated from one another. The leads of the coil preferably extend beyond the back face of the coil and are spaced from one another. The cable is preferably a triaxial cable comprised of an outer protective jacket circumscribing an interior of the cable which includes three concentrically disposed conductors separated from one another by at least two concentrically disposed insulators. Specifically, the outer protective jacket circumscribes the concentrically disposed triaxial, coaxial and center conductor which are separated from one another by an insulator and a dielectric interposed between the triaxial and coaxial conductors and the coaxial and center conductors, respectively. The dielectric is preferably formed from Teflon® which has been etched.

At least one end of the cable is stripped in a steplike fashion to expose a length of the center conductor, the dielectric, the coaxial conductor, the insulator and the triaxial conductor. In addition, the encapsulated transducer includes a front ferrule having a bore with an inner diameter substantially equal to the outer diameter of the center conductor and a rear ferrule having a bore with an inner diameter substantially equal to the outer diameter of the coaxial conductor. The front and the rear ferrules are then inserted onto the stripped end of the cable and soldered to the center conductor and the coaxial conductor respectively.

Once the solder has made a permanent mechanical and electrical connection between the front and rear ferrules and the respective conductors, the sensing coil is resistance welded to the ferrules. This is accomplished by resistance welding one lead of the coil to the front ferrule and the other lead of the coil to the rear ferrule.

Once the process of electrically and mechanically coupling the coil to the cable is completed, the coil is located within a mold and then an alignment plug is molded over the coil and cable. Specifically, the coil is located within the mold by placing the coil on a pin of the mold such that the pin is received within the center void of the coil. The pin supports the coil and axially aligns the coil with respect to the leading portion of the cable operatively coupled to the coil. Moldable material is then emitted into the mold to ensconce the coil and the leading portion of the cable thus forming the alignment plug. A portion of the mold or an insert abuts against the front face of the coil to prevent the moldable material from covering the front face of the coil while forming the alignment plug. In addition, the mold is provided with protrusions which form corresponding indentations in the alignment plug. The indentations are precisely located at a predetermined distance from the front face of the coil to effectively locate the aligned coil and cable assembly in an injection mold.

The injection mold is defined by an upper mold plate having an upper cavity and a lower mold plate having a lower cavity. The upper and lower cavities form a mold cavity when in the closed position which is complementary to the desired form of the encapsulation of the aligned coil and cable assembly. The mold cavity is defined by an upper wall, a lower wall, a front wall and a back wall having an opening extending therethrough. Preferably, the upper mold plate and the lower mold plate are each provided with at least one slideable support pin which extends into the respective upper or lower cavity of the mold and when retracted conforms to the desired shape of the respective upper or lower wall of the mold cavity. In addition, a slideable locator pin is provided adjacent the front wall of the cavity and is capable of telescoping into and out of the cavity when the mold is in the opened position. Preferably, the locator pin is comprised of a pair of concentrically disposed pins in which an inner pin extends further into the cavity than an outer pin.

The aligned coil and cable assembly is placed into the lower cavity of the lower mold plate such that the cable of the aligned coil and cable assembly extends out the opening of the back wall of the mold cavity. The coil of the assembly is centered by way of the slideable locator pin extending into the lower cavity and having the outer pin abutting the front face of the coil and the inner pin being received within the void of the coil. In addition, at least one slideable support pin is extended into the lower cavity and placed in engagement with at least one indentation provided in the alignment plug for supporting and locating the aligned coil and cable assembly. Note that once the slideable locator pin has centered the coil and spaced it a predetermined distance from the front wall of the mold cavity it is withdrawn and the injection mold is closed. The slideable support pin in the upper mold plate is extended into the upper mold cavity and comes into engagement with the indentation provided in the alignment plug when the injection mold is closed. This provides additional means for supporting and locating the coil and cable assembly within the mold cavity such that there is a void completely surrounding the assembly (except of course where the pins are touching the assembly). Note that the location and the number of the slideable support pins may be configured to best support the assembly being encapsulated within the cavity.

Once the mold is in the closed position a self-bonding moldable material is injected into the mold cavity via runners and gates. This process is continued until the mold cavity is completely filled and the coil and cable assembly is completely ensconced within the moldable material. The slideable support pins are then retracted flush with the respective upper and lower walls of the mold cavity prior to the moldable material solidifying. Note that an additional charge of moldable material may be injected into the mold as the support pins are being withdrawn so as to accommodate for any additional material needed to completely fill the voids left by the previously extended support pins. Once the process of injecting the moldable material into the cavity is completed and the support pins have been retracted, the mold may be opened and the encapsulated transducer allowed to cool in the lower mold plate. Once the encapsulated transducer is cooled one or more bottom support pins may be actuated to eject the encapsulated transducer therefrom.

Preferably, the moldable material is polyphenylene sulfide (PPS) and includes a percentage of Teflon®. The Teflon® provides a strong bond between the encapsulation and the etched Teflon® dielectric of the cable. In addition, the rear ferrule includes a shoulder which firmly anchors the coil and cable assembly within the encapsulation for resisting axial forces applied to the encapsulation and/or cable.

OBJECTS OF THE INVENTION

A primary object of the present invention is to provide a new and novel encapsulated transducer with an alignment plug and a method of manufacturing same.

A further object of the present invention is to provide an encapsulated transducer as characterized above which has an injection molded encapsulation ensconcing a sensing coil at one end and a cable extending out of the other end, one end of the cable being electrically connected to the sensing coil within the encapsulation and the other end connected to an electrical processing unit distal from said encapsulation.

Another further object of the present invention is to provide an encapsulated transducer wherein the encapsulation provides a seamless sealing envelope around the sensing coil and an end portion of the cable thus providing an impervious seal against any mechanical, physical or chemical aggressions from the surrounding medium.

Another further object of the present invention is to provide an encapsulated transducer as characterized above wherein the coil and cable are centered within the encapsulation and wherein a distance between the front face of the sensing coil and a front face of the encapsulation is held to a very close tolerance which is reproducible from one transducer to another in mass production.

Another further object of the present invention is to provide an encapsulated transducer as characterized above which is comparatively less expensive to manufacture than existing transducers for use in monitoring and diagnosing the status of rotating and reciprocating machinery and which also lends itself to rapid mass production techniques.

Another further object of the present invention is to provide the alignment plug which axially aligns the sensing coil with respect to the leading portion of the cable operatively coupled to the coil.

Another further object of the present invention is to provide an encapsulated transducer wherein the encapsulation precludes fluid from permeating therethrough and being wicked up by the cable and transported from within a machine environment to the outside environment where it becomes a source of pollution.

Another further object of the present invention is to provide an encapsulated transducer wherein the encapsulation strongly bonds to a dielectric of the cable for providing a leak tight seal and resisting axial forces.

Another further object of the present invention is to provide an encapsulated transducer having an electrical connection between at least one lead of the sensing coil and at least one conductor of the cable which provides internal connection strength which anchors the cable within the encapsulation for resisting axial forces applied to the encapsulation or cable which may cause the electrical connections to completely or partially break resulting in an inoperative or unreliable transducer.

Another further object of the present invention is to provide an encapsulated transducer which is able to be mass-produced with reproducible operational characteristics without appreciable alterations of the signal they emit when in operation.

Another further object of the present invention is to maintain a predetermined linear range capability for each manufactured transducer.

Another further object of the present invention is to provide a slideable location pin which centers and locates the coil within the mold cavity prior to the injection molding process.

Another further object of the present invention is to provide a plurality of slideable support pins for supporting and centering the coil and cable assembly during the injection molding process.

Another further object of the present invention as characterized above is to provide an injection molding step which forms the encapsulation of the sensing coil and an end portion of the cable.

Viewed from a first vantage point, it is an object of the present invention to provide a transducer for monitoring the status of rotating equipment, comprising in combination: a sensing element; first and second leads extending from the sensing element; a cable operatively coupled to the leads, an alignment plug capturing the sensing element and a portion of the cable, and a monolith of cured moldable material ensconcing the sensing element and a portion of the cable defining a seamless mass circumscribing the sensing element and a portion of the cable.

Viewed from a second vantage point, it is an object of the present invention to provide an encapsulated transducer for use in monitoring the status of rotating equipment in a harsh environment with an alignment plug having a leading end with an active element and a trailing end with an information transmitting medium emanating therefrom, formed by: integrally forming a locating means proximate the active element; locating the active element in a mold cavity with the locating means coupled thereto, assuring proper registry in the mold cavity; integrally forming a supporting means proximate the alignment plug; further supporting and locating the active element and the alignment plug in the mold cavity with the support means and removing the locator means; molding over the active element, the alignment plug and a portion of the information transmitting medium with a moldable material except for an area of support; removing the support means; injecting moldable material adjacent the support means for filling in the areas heretofore occupied by the support means; whereby the active element is precisely located in a moldable material to accurately address the rotating equipment.

Viewed from a third vantage point, it is an object of the present invention to provide a transducer for monitoring the status of rotating equipment wherein a shaft of the rotating equipment is exposed to the transducer, comprising, in combination: means for mounting the transducer a distance from the shaft such that a tangent of the shaft is perpendicular to a long axis of the transducer, the transducer having a sensing coil located proximate the shaft, a front portion of the transducer including a protective wall having uniform thickness along a forwardmost portion of the sensing coil, the sensing coil symmetrically disposed about the long axis, and a protective seamless encapsulation integrally formed with the protective front wall ensconcing the sensing coil and a leading portion of a cable operatively coupled to the sensing coil, an alignment plug embedded within the encapsulation and uniting the coil to the cable, and the cable extending away from the transducer to an electrical processing unit.

Viewed from a fourth vantage point, it is an object of the present invention to provide a transducer formed from injection molding, the forming steps including: attaching a coil to a conductor of a cable via an alignment plug, centering the coil within a mold cavity with a coil support, supporting the cable within the mold cavity with plural cable supports, orienting the cable to extend out from the mold cavity, retracting the coil support, injecting moldable material into the cavity of the mold to precisely ensconce the coil and the conductor, retracting the plural cable supports from the cable after the moldable material has been injected into the mold cavity, injecting moldable material adjacent the cable supports for filling in the areas heretofore occupied by the plural cable supports, allowing the moldable material to set, removing the thus-formed transducer from the mold as an integrated unit.

These and other objects will be made manifest when considering the following detailed specification when taken in conjunction with the appended drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of an encapsulated transducer with an alignment plug according to the present invention which is juxtaposed to a rotating shaft of a machine for monitoring the vibration thereof.

FIG. 2 is a partial sectional view of the encapsulated transducer with the according to the present invention.

FIG. 3 is an exploded parts view of a portion of FIG. 2 illustrating certain parts in section.

FIG. 4 is a diagrammatic view of an assembly step of the present invention and an elevational view of the combination of elements as shown in FIG. 3.

FIG. 5 is a elevational view of a sensing coil and cable assembly formed by the combination of elements as shown in FIG. 4.

FIG. 6 is a partial sectional view of the alignment plug formed with the combination of elements as shown in FIG. 5.

FIG. 7 is a simplified cross-sectional view of a mold in an open position and having all included slideable support and locator pins in an extended position.

FIG. 8 is a view of the mold with the slideable support pins centering and supporting that which is shown in FIG. 6.

FIG. 9 is a simplified cross-sectional view of the mold in a closed position with the slideable locator pin retracted from engagement of the sensing coil.

FIG. 10 is a simplified cross-sectional view of the mold in a closed position with the slideable support pins retracted after an injection molding according to the present invention is completed.

FIG. 11 is an elevational view of an injection mold used to mass produce a plurality of encapsulated transducers sequentially.

DESCRIPTION OF PREFERRED EMBODIMENTS

Considering the drawings, wherein like reference numerals denote like parts throughout the various drawing figures, reference numeral 10 is directed to the encapsulated transducer according to the present invention.

In essence, and referring to FIG. 2, the encapsulated transducer 10 includes an injection molded encapsulation 20 having a front end 22 and a back end 24. The encapsulation 20 is a monolith of cured moldable material ensconcing a sensing element 40 proximate the front end 22 and a portion of an information transmitting medium 60 emanating from the back end 24. The sensing element or coil 40 is electrically and mechanically connected to the information transmitting medium or cable 60 by a pair of suitably sized front and rear ferrules 80, 90 secured to a center and coaxial conductor 66, 70 of the associated cable 60 thereby forming a coil and cable assembly 110 (FIG. 5). An alignment plug 120 is symmetrically disposed within the encapsulation 20 and aligns the coil 40 along a long axis “A” of the transducer 10 thereby forming an aligned coil and cable assembly 140 (FIG. 6). In addition, the alignment plug 120 rigidly spaces the coil 40 a predetermined distance from the front ferrule 80. At least the rear ferrule 90 includes a shoulder 100 for firmly anchoring the coil and cable assembly 110 within the encapsulation 20. In addition an injection molding process provides the durable encapsulation 20 which bonds with itself and with a dielectric 68 of the cable 60 and symmetrically locks the aligned coil and cable assembly 140 therein.

More specifically, and referring to FIG. 3, the cable 60 is preferably a triaxial cable comprised of an outer jacket 76 circumscribing an interior of the cable which includes three concentrically disposed conductors 66, 70 and 74 separated from one another by at least two concentrically disposed dielectrics or insulators 68, 72. Particularly, the outer protective jacket 76 circumscribes the concentrically disposed triaxial, coaxial and center conductors 74, 70 and 66 which are separated from one another by an insulation 72 and a dielectric 68 interposed between the triaxial and coaxial conductors 74, 70 and the coaxial and center conductors 70, 66, respectively. The coaxial and triaxial conductors 70, 72 are preferably braided conductors. The dielectric 68 is preferably made from a Teflon® material which has been etched for bonding purposes. As shown in FIG. 3, at least one end 62 of the cable 60 is stripped in a steplike fashion to expose a length of the center conductor 66, the dielectric 68, the coaxial conductor 70, the insulator 72 and the triaxial conductor 74.

Referring to FIGS. 3 and 4, the rear ferrule 90 includes a bore 96 with an inner diameter substantially equal to an outer diameter of the coaxial conductor 70. The rear ferrule 90 is preferably connected to the coaxial conductor 70 such that an end 94 of the rear ferrule 90 abuts the insulator 72. The front ferrule 80 includes a bore 86 with an inner diameter substantially equal to the outer diameter of the center conductor 66. The front ferrule 80 is connected to the center conductor 66 such that a back end 84 of the front ferrule 80 abuts the dielectric 68 of the cable 60.

The process of electrically and mechanically connecting the front and rear ferrules 80, 90 to their respective conductors 66, 70 is as follows. A preformed rear solder ring 98 is inserted onto the stripped end 62 of the cable 60 such that it encircles the coaxial conductor 70 and abuts against the coaxial insulator 72. The rear ferrule 90 is then inserted onto the stripped end 62 of the cable 60 such that it encircles the coaxial conductor 70 and comes into engagement with the preformed rear solder ring 96. A preformed front solder ring 88 is then inserted onto the stripped end 62 of the cable 60 such that it encircles the center conductor 66 and abuts against the dielectric 68. The front ferrule 80 is then inserted onto the stripped end 62 of the cable 60 such that it also encircles the center conductor 66 and comes into engagement with the preformed front solder ring 88. This completed cable assembly is positioned in an inductive heating unit where the solder rings 88, 98 are melted and permeate into the adjacent areas between the bores 86, 96 of the front and rear ferrules 80, 90 and the center and coaxial conductors 66, 70 respectively. When the preformed front and rear solder rings 88, 98 have melted a small amount of axial force is applied to the front and rear ferrules 80, 90 so that the back end 84 of the front ferrule 80 abuts against the dielectric 68 and the back end 94 of rear ferrule 90 abuts against the coaxial conductor 70. Once the solder is cooled it locks the rear ferrule 90 to the coaxial conductor 70 and the front ferrule 80 to the center conductor 66 in a spaced coaxial proximity from one another. Preferably, both ferrules 80, 90 are formed from brass. In addition, the use of preformed solder rings 88, 98 helps to provide effective repeatability of the electromagnetic characteristics of the encapsulated transducer 10 especially with respect to the inductance parameter of the sensing coil 40.

Once a permanent mechanical and electrical connection has been made between the front and rear ferrules 80, 90 and the respective conductors 66, 70, the sensing coil 40 is resistance welded to the front and rear ferrules 80, 90. Referring to FIGS. 4 and 5, the sensing coil 40 includes a front face 44, a back face 46 and a body 52 having an outer surface 54 and a center void extending therethrough. The body 52 extends between the front face 44 and the back face 46. A first lead 48 and a second lead 50 extends beyond the back face 46 of the coil 40 and are spaced a part from one another. The coil 40 and the cable 60 are supported by a fixture (not shown) so that the back face 46 of the coil 40 and a front end 82 of the front ferrule 80 are held at a constant distance “X” (FIG. 5). The fixture substantially maintains this distance “X” when the first lead 48 is resistance welded to the front ferrule 80 and the second lead 50 is resistance welded to the rear ferrule 90. As noted above, resistance welding is used to connect the leads 48, 50 to the respective ferrules 80, 90 however, solder or laser welding may also be used.

Referring to FIG. 7, once the process of electrically and mechanically coupling the coil 40 to the cable 60 is completed, the coil 40 is located within a mold, for example, mold 150 having an upper and lower cavity 152, 154 shaped complementary in form to an alignment plug 120 which is molded over the coil 40 and cable 60. Specifically, the coil 40 is located within the mold by placing the coil 40 on a pin of the mold such that the pin is received within the center void 42 of the coil 40. The pin supports the coil 40 and axially aligns the coil 40 with respect to the leading end 62 of the cable 60 operatively coupled to the coil 40. Moldable material is then emitted into the mold to ensconce the coil 40 and a portion of the leading end 62 of the cable 60. Referring to FIG. 7, a portion of the mold or an insert abuts against the front face 44 of the coil 40 to preclude the moldable material from contacting or covering the front face 44 of the coil 40 while forming the alignment plug 120 (please see FIG. 6). In addition, the mold is provided with protrusions which form the corresponding indentations 136 a, 136 b in the alignment plug 120. The indentations 134 a, 134 b are precisely located at a predetermined distance from the front face 44 of the coil 40 to effectively locate the aligned coil and cable assembly 140 in an injection mold 150 (please see FIG. 7). Moreover, the constant distance “X” between the back face 46 of the coil 40 and the front end 82 of the front ferrule 80 is rigidly maintained by the alignment plug 120. Thus, the distance “X” between the back face 46 of the coil 40 and the remaining metal portions of the coil and cable assembly 110 provide an electromagnetic relationship of the coil 40 which is repeatedly and precisely fixed.

The alignment plug 120 includes a front end 122 having an annular recess 124 defined by a center post 126 and an outer peripheral wall 128. The center post 126 extends within the center void 42 of the coil 40 and the outer peripheral wall 128 contacts and contours to the outer surface 54 of the coil 40 and uniformly extends parallel to an outer surface 134. The alignment plug 120 further includes a back end 130 circumscribing a length of the leading end 62 of the cable 60 and a medial portion 132 integrally formed with and interposed between the front end 122 and the back end 130 of the alignment plug 120.

Referring to FIGS. 7 through 9, the injection mold 150 is defined by an upper mold plate 152 having an upper cavity 154 and a lower mold plate 156 having a lower cavity 158 forming a single mold cavity 160 when in the closed position. The mold cavity 160 is shaped complementary to the desired form of the encapsulation 20 of the aligned coil and cable assembly 140. The mold cavity 160 is defined by an upper wall 162, a lower wall 164, a front wall 166 and a back wall 168 having an opening 170 extending therethrough (FIG. 9).

The upper mold plate 152 is provided with at least one sleeve 182 a through which at least one slideable support pin 180 a may be moved into or out of the upper cavity 154 by a drive means 200 a. The lower mold plate 156 is provided with at least one sleeve 182 b through which at least one slideable support pin 180 b may be moved into or out of the lower cavity 158 by corresponding drive means 200 b. In addition, the injection mold 150 is provided with a slideable locator pin 190 which is preferably disposed on the lower mold plate 156 at a location adjacent the front wall 166 of the mold cavity 160. The slideable locator pin 190 preferably includes a pair of concentrically disposed slideable pins 192, 194 in which an inner pin 192 slides within an outer pin 194 which in turn slides within a sleeve 196. Both the inner pin 192 and the outer pin 194 may be moved by an associated drive means 200 c such that they are capable of extending into or out of the lower cavity 158 when the mold 160 is in the opened position. Preferably, the inner pin 192 is capable of extending further into the lower cavity 158 than the outer pin 194.

Alternatively, the slideable locator pin 190 may be an integrally formed T-shaped pin having a top branch resembling the outer pin 194 and a base branch resembling the inner pin 192 in an extended and rigidly fixed position with respect to the top branch.

The slideable support pins 180 a, 180 b and the slideable locator pin 190 are each preferably provided with separate drive means, 200 a-200 c respectively and may be independently controlled by a programmable logic controller (PLC) 230 or the like.

Each drive means 200 a-200 c includes a valve and solenoid unit 202 a-202 c, a pneumatic cylinder 204 a-204 c and an ejector plate 206 a-206 c. Each ejector plate 206 a, 206 b is connected to each respective slideable support pin 180 a, 180 b and ejector plate 206 c is connected to the slideable locator pin 190. Each ejector plate 206 a-206 c is received within the corresponding pneumatic cylinder 204 a-204 c which in turn is connected to the corresponding valve and solenoid unit 202 a-202 c. Each valve and solenoid unit 202 a-202 c is electrically connected to the PLC 230 and mechanically connected to a gas source 220. The PLC 230 independently sends out an electrical signal to each solenoid of each valve and solenoid unit 202 a-202 c. Each solenoid receives the signal and physically opens and closes the corresponding valve. This allows gas to be sent to each respective pneumatic cylinder 204 a-204 c and depending on the location of each ejector plate 206 a-206 c will cause each slideable support pin 180 a, 180 b and slideable locator pin 190 to extend into or retract out of the mold cavity 160. The ejector plate 206 c may be coupled to the inner pin 192 such that the inner pin 192 extends or retracts a short distance and then catches the outer pin 194 and causes it to correspondingly extend or retract.

When the injection mold 150 is in the closed position only the slideable support pins 180 a, 180 b are used to support and symmetrically locate the aligned coil and cable assembly 140 within the mold cavity 160 (FIG. 9). Depending upon the configuration of the specific assembly 140 and the way molten plastic is filling around the assembly 140, one of the slideable support pins may be retracted sooner than another. Retracting the core pins is sequenced with the timing in the PLC 230 and may be calibrated until all of the slideable support pins 180 a, 180 b retract in a manner which allows the assembly 140 to remain centered both radially and axially within the mold cavity 160. Note that if the retraction of the slideable support pins 180 a, 180 b is not sequenced correctly the assembly 140 may shift to one side or the other in the mold cavity 160. This may cause an alteration of the electrical characteristics of the encapsulated transducer 10.

Referring to FIG. 7, the aligned coil and cable assembly 140 is radially and axially centered by way of the extended slideable support pins 180 a, 180 b and an extended slideable locator pin 190. The locator pin 190 centers the coil 40 and spaces it a predetermined distance from the front wall 166 of the mold cavity 160 by way of the inner pin 192 being received within the center void 42 of the coil 40 and the outer pin 194 abutting against the front face 44 of the coil 40. In addition, the slideable support pin 180 b is extended into the lower cavity 158 and received within the indentation 136 b for providing support thereto. Once the aligned coil and cable assembly 140 has been centered within the lower cavity 158, the locator pin 190 is withdrawn and the mold 150 is placed in a closed position (FIG. 9). At this time, the front face 44 of the coil 40 is precisely spaced from the front wall 166 of the mold cavity 160. This allows the encapsulated traducers 10 to include a substantially constant face thickness “T” (FIG. 2) and thus, a predetermined linear range. This is particularly important when manufacturing a plurality of encapsulated transducers 10 which are to include the same electrical characteristics. Furthermore, once the mold 150 is closed the cable 60 extends out of the opening 170 in the back wall 168 of the mold cavity 160. The engagement of the upper mold plate 152 and the lower mold plate 156 provides additional support by having the cable 60 cantilevered therebetween. The slideable support pin 180 a extends into the upper cavity 154 from the upper mold plate 152 and comes into engagement with the indentations 136 a of the alignment plug 120 thereby providing a top support to the aligned coil and cable assembly 140. A void completely surrounds the aligned coil and cable assembly 140 except of course where the support pins 180 a, 180 b are abutting the assembly 140. An alternative embodiment to FIG. 9 may use fewer or more core pins 180 a, 180 b for centering and supporting the aligned coil and cable assembly 140 in the mold cavity 160.

The moldable material is injected into the mold cavity via runners 200 and gates 202 provided in the lower mold plate and/or the upper mold plate. Preferably, the moldable material includes polyphenylene sulfide (PPS) and includes a percentage of a Teflon® material. In addition, preferably twenty percent by weight of Teflon® is introduced into the moldable material in order to provide a means for providing a strong bond between the encapsulation 20 formed by the moldable material and the etched Teflon® dielectric 68 of the cable 60. The injection of the moldable material is continued until the mold cavity 160 is completely filled. Once the mold cavity 160 is filled, the support pins 180 a, 180 b are sequentially retracted such that the aligned coil and cable assembly 140 remains centered within the mold cavity 160. Note that an additional charge of moldable material may be introduced into the mold cavity 160 simultaneously with the retractions of the support pins 180 a, 180 b such that the aligned coil and cable assembly 140 is completely ensconced within the moldable material and all voids have been filled.

Referring to FIG. 10, once the process of injecting the moldable material into the mold cavity 160 is completed and the support pins 180 a, 180 b have been retracted, the mold 150 may be opened and the encapsulated transducer 10 allowed to cool in the lower mold plate 156. Once the encapsulated transducer 10 is cooled the bottom support pin 180 b may be actuated to eject the encapsulated transducer 10 therefrom.

In mass production it is preferred that an injection molding device be provided which includes a single upper mold plate 152 and a plurality of lower mold plates 156 disposed on a rotatable table 240. The lower plates 156 may each be preloaded with a single aligned coil and cable assembly 140. Then, the upper mold plate 152 comes down onto the first inline lower mold plate 156 and the respective aligned coil and cable assembly 140 is encapsulated. Once the encapsulation process is completed the upper mold plate 152 is lifted and the table 240 is rotated to align a subsequent lower mold plate 156 with the stationary upper mold plate 152 so that the encapsulation process may be repeated. This process may continue for encapsulating a batch of aligned coil and cable assemblies 140.

After the encapsulation process is complete and the upper mold plate 152 is lifted from the lower mold plate 156, the table 240 is rotated and the corresponding encapsulated transducer 10 remains within the lower mold plate 156. For example, if the encapsulation processes is completed at a twelve o'clock position on the rotatable table 240 the encapsulated transducer 10 may remain within the lower mold plate 156 and allowed to cool until the table 240 has rotated from the twelve o'clock position to a six o'clock position were it ejected as delineated above. Now, after the encapsulated transducer 10 is ejected from the lower mold plate 156 the lower mold plate is reloaded with an aligned coil and cable assembly 140 and extends from the six o'clock position back to the twelve o'clock position as the table 240 is rotated.

In use and operation, and referring to FIGS. 1 and 2, the encapsulated transducer 10 may, for example, be utilized as a proximity transducer for monitoring the vibrational characteristics of a rotating shaft 252 of a machine 250. In this environment the encapsulated transducer 10 operates on the eddy current principle and outputs a signal correlative to the spacing between the rotating shaft 252 and the sensing coil 40 of the encapsulated transducer 10.

Typically, the encapsulated transducer 10 is circumscribed by a threaded metal case 254 which is mounted adjacent the rotating shaft of the machine 250. A mounting means 256 is used to strategically mount the encapsulated transducer 10 a distance from the shaft such that a tangent of the shaft is perpendicular to the long axis “A” of the encapsulated transducer 10. The sensing coil 40 is electrically and mechanically connected to the cable 60. The cable 60 extends out the back end 24 of the encapsulation 20 and runs through a casing 258 of the machine 250 where it preferably terminates to a connection 260 capable of directly coupling to the electrical processing unit 280 or to an extension cable which in turn couples to the electrically processing unit 280.

Preferably, the cable is routed through the machine case 254 by passing through a rubber grommet 264 internal to an adaptor 262 operatively coupled to the machine case 258. The adaptor 262 includes a first end 266 having external and internal threads. The external threads of the adaptor are coupled with a threaded bore 270 in the machine case 258 for firmly connecting the adaptor thereto. In some instances, the internal threads of the first end of the adaptor allow the mounting of the encapsulated transducer 10 via the threaded metal case 254. A second end 268 of the adaptor 262 having external threads may be coupled to a threaded aperture 274 in a junction box 272 such that the junction box is mounted to the machine case 258. The junction box 272 allows any electrical connections operatively coupling the cable 60 to the electrical processing unit 270 to be enclosed in a weather-proof or explosion-proof environment.

In addition to use as a proximity transducer, the present invention may be employed very broadly in the monitoring and diagnosing the status of rotating and reciprocating machinery. One example is as a temperature transducer which would use a coil formed from a single wire thermocouple of the RTD type. The coil would be molded within the encapsulation 20 and the only change in the above delineated process may be in the use of perhaps a thinner overall encapsulation. This would provide for a suitable heat transfer to the RTD temperature sensing coil.

Moreover, having thus described the invention, it should be apparent that numerous structural modifications and adaptations may be resorted to without departing from the scope and fair meaning of the instant invention as set forth hereinabove and as described hereinbelow by the claims. 

I claim:
 1. A method for making a transducer, the steps including: providing an air core coil having a hollow interior defining a center void and first and second leads extending from said coil; connecting said leads of said coil to conductors of a leading portion of a cable; forming an alignment plug including molding a front end flush with a front face of said air core coil without covering said front face of said air core coil, molding a back end over a length of said leading portion of said cable and, molding a medial portion contacting and contouring to an entire back face of said air core coil and integrally formed with and interposed between said front end and said back end of said alignment plug for capturing said air core coil and said leading portion of said cable, said medial portion of said alignment plug including an integrally formed outer peripheral wall contacting and contouring to an exterior surface of said air core coil and extending substantially parallel thereto, and molding a center post integrally formed with said medial portion of said alignment plus and extending a distance into said center void of said air core coil, said outer peripheral wall, said medial portion and said center post defining an annular recess integrally formed in said alignment plug and contacting and contouring to said exterior surface, said back face and a first portion of said center void of said air core coil; leaving a second portion of said center void of said air core coil unfilled with said alignment plug; aligning said alignment plug within an injection mold cavity with an axially slidable support being received within said unfilled portion of said center void of said air core coil; subsequently retracing said axially slidable support and injection molding a uniform uninterrupted front wall immediately forward said air core coil and a body over an entirety of said alignment plug and a portion of said cable defining a mass ensconcing said air core coil, said alignment plug and said leading portion of said cable.
 2. The method claim 1 wherein said one piece alignment plug molding step further includes the step of spacing said coil away from said leading portion of said cable at a known predetermined repeatable distance.
 3. The method of claim 2 wherein said one piece alignment plug molding step further includes axially aligning said coil with said leading portion of said cable.
 4. The method of claim 3 wherein said one piece alignment plug molding step further includes maintaining the precise spacing and axial alignment of said coil with respect to said leading end of said cable while curing the alignment plug for providing an electromagnetic relationship of said coil and cable which is repeatable and rigidly maintained.
 5. The method of claim 4 wherein said one piece alignment plug molding step further includes the step of supporting said cable within the mold cavity with at least one retractable cable support and axially aligning said coil with respect to said leading end of said cable.
 6. The method of claim 5 wherein said injection molding step further includes a step of orientating and supporting said alignment plug in an injection mold cavity by registering at least one slideable support integrally formed within the mold cavity with at least one integrally formed indentation within said alignment plug and spacing said front face of said coil a precise length from a front wall of the injection mold cavity for controlling the thickness of said uniform uninterrupted from wall immediately forward said coil.
 7. The method of claim 6 wherein the injection molding step further includes retracting said at least one slidable support supporting said alignment plug after the moldable material has been injected into said injection mold cavity.
 8. The method of claim 7 wherein said injection molding step further includes injecting moldable material adjacent said at least one slidable support for filling in the area heretofore occupied by said at least one slidable support.
 9. The method of claim 8 further including the step of allowing the injected moldable material to set and removing the thus formed transducer from the mold as an integrated unit.
 10. The method of claim 1 wherein the step of connecting said leads of said coil to conductors of a cable includes the step of providing a cable having at least one outer conductor surrounding at least one insulator carrying at least one center conductor and stripping an end of said cable in a step like fashion to expose a portion of said center conductor, said insulator and said outer conductor.
 11. The method of claim 10 wherein said connecting step further includes the step of forming a front and rear pair of ferrules with said front ferrule having a bore with a diameter substantially matching the diameter of said center conductor and said rear ferrule having a bore with diameter substantially matching the diameter of said outer conductor.
 12. The method of claim 11 wherein the connecting step further includes attaching said front ferrule to said center conductor and said rear ferrule to said outer conductor of said stripped end of said cable.
 13. The method of claim of 12 wherein connecting said leads of said coil to conductors of said cable further includes connecting said first lead to said front ferrule and said second lead to said rear ferrule.
 14. The method of claim 13 wherein said one piece alignment plug molding step includes axially aligning said coil along a long axis of said transducer and spacing said coil away from said stripped end of said cable at a known predetermined repeatable distance.
 15. The method of claim 14 wherein said one piece alignment plug molding step further includes molding said alignment plug over an outer periphery and back face of said coil, over said first lead and front ferrule and over at least a portion of said second lead and said insulator to rigidly maintain said precise distance between said coil and said stripped end of said cable for providing a electromagnetic relationship of said coil and cable which is repeatable and precisely fixed.
 16. The method of claim 1 wherein said one piece alignment plug molding step further includes providing at least one indention in a medial portion of said alignment plug which is at a precise length from said front face of said coil.
 17. The method of claim 16 further including the step of orientating and supporting said alignment plug in an injection mold cavity by registering at least one slideable support integrally formed within the injection mold cavity with at least the one said indentation integrally formed in said one piece alignment plug.
 18. The method of claim 17 further including the step of supporting said cable within the mold cavity with at least one slideable support integrally formed within the injection mold cavity and orientating the cable to extend out from the mold cavity.
 19. The method of claim 18 wherein said injection molding step includes the step of injecting moldable material into the injection mold cavity to precisely ensconce said alignment plug, said rear ferrule and said portion of said cable adjacent thereto wherein the moldable material contacts and contours to said front face of said coil and uniformly extends therefrom to form said uniform uninterrupted front wall substantially parallel with said front face of said coil.
 20. The method claim 19 further including the step of retracting said alignment plug and cable supports after the moldable material has been injected into the mold cavity and subsequently injecting moldable material adjacent the supports for filling in the area heretofore occupied by said supports.
 21. The method of claim 20 further including allowing the moldable material to set and removing the thus formed transducer from the mold as an integrated unit.
 22. A method for making a transducer, the steps including: attaching an air core coil having a hollow interior defining a center void to a conductor of a leading portion of a cable; forming an alignment plug including molding a front end flush with a front face of said air core coil without covering said front face of said air core coil molding a back end over a length of said leading portion of said cable and, molding a medial portion contacting and contouring to an entire back face of said air core coil and integrally formed with and interposed between said front end and said back end of said alignment plug for capturing said air core coil and said leading portion of said cable, said medial portion of said alignment plug including an integrally formed outer peripheral wall contacting and contouring to an exterior surface of said air core coil and extending substantially parallel thereto, and molding a center post integrally formed with said medial portion of said alignment plug and extending a distance into said center void of said air core coil, said outer peripheral wall, said medial portion and said center post defining an annular recess integrally formed in said alignment plug and contacting and contouring to said exterior surface, said back face and a first portion of said center void of said air core coil; leaving a second portion of said center void of said air core coil unfilled with said alignment plug; aligning said alignment plug within an injection mold cavity with an axially slidable support being received within said unfilled portion of said center void of said air core coil; subsequently retracing said axially slidable support, and supporting and locating said alignment plug within an injection mold cavity with at least one slidable support, assuring proper registry in the injection mold cavity; injection molding a uniform uninterrupted front wall over said front face of said coil and a body over an entirety of said alignment plug and a portion of said cable emanating from said alignment plug with a moldable material except for an area of support; removing at least one said slidable support; injecting moldable material adjacent at least the one said slidable support for filling in the areas heretofore occupied by at least the one slidable support; wherein said coil and alignment plug are ensconced by and precisely located in the moldable material.
 23. The method of claim 22 wherein the supporting and locating step includes the step of locating said coil in the mold cavity with a slideable locating support coupling to said locating means, assuring proper registry in said mold cavity.
 24. The method of claim 22 wherein said supporting and locating step includes the step of supporting and locating said coil and said alignment plug in said mold cavity with said slideable support means coupling to said support receiving means and removing said locating means.
 25. The method of claim 24 wherein said alignment plug molding step includes the step of protecting an outer surface of said coil with an outer peripheral wall integrally formed with said center post and contacting and contouring to an exterior surface of said active element wherein said outer peripheral wall, said center post and a portion of said alignment plug contacting and contouring to a back face of said active element define an annular recess integrally formed in said alignment plug.
 26. A method for making a transducer, the steps including: attaching an active element to a leading portion of a cable; forming an alignment plug including molding a front end flush with a front face of said active element, a back end over a length of said leading portion of said cable and, a medial portion contacting and contouring to an entire back face of said active element and integrally formed with and interposed between said front end and said back end of said alignment plug for capturing said active element and said leading portion of said cable, said medial portion of said alignment plug including an integrally formed outer peripheral wall contacting and contouring to an exterior surface of said active element and extending substantially parallel thereto, and a center post integrally formed with said medial portion of said alignment plug and extending a distance into an air core of said active element, said outer peripheral wall, said medial portion and said center post defining an annular recess integrally formed in said alignment plug and contacting and contouring to said exterior surface, said back face and a portion of said air core of said active element, integrally forming a locating means proximate said active element; locating said active element in a mold cavity with said locating means coupled thereto, assuring proper registry in said mold cavity; integrally forming a supporting means proximate said alignment plug; further supporting and locating said active element and said alignment plug in said mold cavity with said supporting means and removing said locating means; molding over said active element, said alignment plug and a portion of said information transmitting medium with a moldable material except for an area of support; removing said supporting means; injecting moldable material adjacent said supporting means for filling in the areas heretofore occupied by said supporting means; whereby said active element is precisely located in a moldable material.
 27. The method of claim 26 wherein the step of locating said active element in said mold cavity includes the step of receiving said locating means within a center void of said active element.
 28. The method of claim 27 further including the step of providing grooves in said alignment plug at a precise length from a front face of said active element.
 29. The method of claim 28 wherein the step of further supporting and locating said active element and said alignment plug includes providing support means with a plurality of radially slideable supports and spacing said front face of said active element a precise distance from a front wall of said mold cavity by said grooves receiving said radially slideable supports.
 30. The method of claim 29 further including the step of providing a drive means to the axially slideable support and to the plurality of radially slideable supports for sliding each support into or out of the mold cavity.
 31. The method of claim 30 further including the step of providing a control means for signaling the drive means for independently sliding each support into or out of the mold cavity.
 32. The method of claim 31 further including the step of providing an alterable timing sequence for orchestrating the control means signaling of the drive means. 